A study of photometric observations of (3200) phaethon from Lulin observatory

Abstract The near-Earth asteroid (3200) Phaethon is regarded as the parent body of the Geminid meteor stream. It is also an active asteroid with a very blue spectrum which is similar to that of the members of the Pallas family. For obtaining this asteroid’s surface property in more detail, we conducted a series of multicolor photometry of this asteroid over a wide range of solar phase angle during its close approach to the Earth in the end of 2017. Our observations confirmed that Phaethon is a C-complex asteroid as previous studies have claimed. We also obtained the phase curve for this asteroid in solar phase angle of 22.67 ∼ 114.48 degrees. From this result, we estimate that the absolute magnitude (H) of this asteroid is 14.450±0.017 mag, and its phase slope is (β) ∼0.0423±0.0005. Using the absolute magnitude that we estimated, together with an estimate of Phaethon’s albedo (0.122 ± 0.03) that previous literature derived, we can derived the Phaethon’s diameter, 4. \mathrm{90}_{-0.54}ˆ{+0.79} km. The diameter estimate is roughly consistent with what was observed through the radar ranging measurement conducted as the same period as our observation.